Abrasive wheel having a metal coated graphite lubricant therein



T J. MARTIN Sept. 17, 1968 ABRASIVE WHEEL HAVING A METAL COATED GRAPHITELUBRICANT THEREIN Filed Dec. 7, 1965 Inventor Thomas J. Mar-k in.

United States Patent 3,402,035 ABRASIVE WHEEL HAVING A METAL COATEDGRAPHITE LUBRICANT THEREIN Thomas J. Martin, 97 Dover St., La Grange,Ill. 60525 Filed Dec. 7, 1965, Ser. No. 523,237 Claims. (Cl. 51--298)ABSTRACT OF THE DISCLOSURE A diamond abrasive wheel wherein the diamondparticles are dispersed in a bonding matrix and wherein a compound solidlubricant material for said wheel is defined by graphite particleshaving a metallic coating bonded thereto is dispersed within the wheelin the voids between the diamond abrasive particles whereby, in use, thegraphite lubricant particles are dispensed to permit flow of graphiteover the surface of the wheel.

The present invention relates to an improved abrasive wheel of the typehaving diamond abrasive particles and more particularly it relates to animproved diamond abrasive wheel having a solid lubricant materialtherein. The present invention further relates to a method for thepreparation of the improved abrasive wheel.

One of the significant problems in the use of any grinding or abrasiveWheel resides in the provision of a suitable and constant lubrication inthe interfacial area defined between the abrasive wheel and theworkpiece. It can readily be seen that failure to provide lubrication atthe interface may give rise to damage to the material being worked on orearly deterioration of the abrasive wheel. Failure to suitably lubricatethe interface will result in the generation of high temperatures at theinterface due to the friction between the abrasive wheel and theworkpiece. Water is a commonly used lubricating and cooling material.However, introduction of water at the interface obscures the surface ofthe material being worked on and, accordingly, progress of the work maynot be observed carefully during grinding.

It is well known that graphite is a very good lubricating material. Itshould 'be observed, however, that graphite powder is very light anddifficult to control. For this reason external introduction of graphiteto the work interface between the abrasive wheel and the workpiece isimpractical. Attempts have been made from time to time to introducegraphite into the diamond abrasive section of a diamond grinding wheel.A wheel structure of this type would be very desirable in that theabrasive wheel would carry its own lubricating material and externallubrication of the work interface during use of the wheel would not berequired. However, the attempts to include graphite particles within thediamand abrasive section of the abrasive wheel were generallyunsatisfactory in that the graphite particles would not suitably bondwith any material used in preparation of the abrasive wheel and theresultant structure ws highly unstable. Bonded abrasive sectionsincluding graphite particles as a part of the section had a lowcharacteristic inherent strength which resulted in an unstable abrasivesection. Attempts to bond other good lubricating materials, such asmolybdenum disulfide, into a resin or metal matrix abrasive section wereequally unsuccessful.

The present invention is directed to the provision of an improvedgrinding or abrasive wheel having a graphite lubricant material securedwithin the diamond abrasive section of the grinding wheel. The Wheel ofthe present invention does not have the low inherent strength andinstability characteristic of prior structures where attempts were madeto include graphite as a lubricant within the body of the abrasivewheel. In the structure disclosed herein the graphite lubricantparticles are substantially enveloped with a very thin coating of metal.The metal coating of the graphite core material is compatible witheither a metal or resin matrix material used for containing and bondingthe abrasive particles to the wheel base. In one form of the inventionnickel is employed as the material to define the metal coating about thegraphite particles. A satisfactory envelope thickness is about twomicrons.

The metal coated graphite material is uniformly dispersed throughout theabrasive section defined on the grinding wheel. The metal envelope ofthe graphite lubricating particles bonds securely to the matrix materialin which the abrasive and lubricating particle-s are disposed to definea finished structure that is stable in use and that has high inherentstrength. In use, of course, the graphite lubricating particles will bereleased and will flow over the abrasive particles and between saidabrasive particles and the workpiece to lubricate the interface and toprevent the generation of excessive frictional grinding temperatures. Itshould be observed that if high temperatures are permitted to develop inthe working area the abrasive section of the grinding wheel may rapidlydeteriorate due to a breaking down of the bond between the abrasiveparticles, the matrix in which said particles are dispersed and thewheel base. Thus, the reduction of friction in the interfacial area bylubrication will effectively extend the useful life of the abrasivewheel.

It is, accordingly, a general object of the present invention to providean improved abrasive wheel.

A further object of the present invention resides in the provision of animproved abrasive Wheel of the type having diamond abrasive particles.

Another object of the present invention resides in the provision of animproved diamond abrasive wheel having solid lubricant material disposedwithin the body of the Wheel to obviate the need for externalapplication of a lubricant during use of the wheel.

An additional object of the present invention resides in the provisionof an improved diamond abrasive wheel having diamond abrasive particlesand solid lubricant particles dispersed within a matrix and with thematrix and particles bonded to a wheel base.

A further object of the present invention resides in the provision of animproved diamond abrasive wheel having solid lubricant particles bondedwithin a thermosetting resin matrix whereby during use the lubricantparticles are released to flow over the diamond abrasive particles tolubricate the interface between the abrasive particles and theworkpiece.

Still another object of the present invention resides in the provisionof an abrasive wheel having graphite lubricant particles dispersedwithin the wheel structure which particles are disposed within a metalenvelope material to define a structure that may be bonded to athermosetting resin or other matrix.

An additional object of the present invention resides in the provisionof a method for preparing an abrasive wheel having graphite lubricantparticles therein and wherein the particles are bonded within a matrixmaterial for release during use to flow over the abrasive particles.

Another object of the present invention resides in the provision of amethod for the preparation of an abrasive Wheel wherein diamond abrasiveparticles and metal coated graphite particles are dispersed within andbonded to a thermosetting resin.

The novel features which are believed to be characteristic of thepresent invention are set forth with particularity in the appendedclaims. The invention itself, however, together with further objects andadvantages thereof, will best be understood by reference to thefollowing description taken in connection with the accompanyingdrawings, in which:

FIGURE 1 is a top plan view of a mold with a premachined wheel baseelement which assembly is adapted for use in preparation of the abrasivewheel described herein;

FIGURE 2 is .a side view, in section, of the mold and wheel baseassembly of FIGURE 1 showing the matrix, abrasive particle and lubricantparticle mixture disposed in a recess in the wheel base and illustratingcompression of the mixture on to the wheel base;

FIGURE 3 is a side view, in section. of the abrasive wheel of thepresent invention in one stage of processing with the abrasive materialssection compressed into the wheel base recess, said arbasive materialssection being bonded to the wheel base at this stage of processing;

FIGURE 4 is a side view, in section, of the wheel of FIGURE 3 with thecentral portion of the wheel base removed and the wheel in condition foruse;

FIGURE 5 is a schematic representation of the abrasive materials sectionof the grinding wheel showing the abrasive particles and metal coatedgraphite lubricating particles interspersed within the matrix; and

FIGURE 6 is an enlarged schematic representation, in section, of agraphite particle showing a portion of the metal envelope about saidparticle.

The method of making the abrasive wheel of the present invention will bediscussed in connection with the preparation of a diamond abrasive wheelwith the abrasive section thereof being secured to an aluminum base.While the ratio of ingredients included in the abrasive section may varyit should be noted that the compression forces, the temperatures, thebonding and curing cycles (or sintering cycle when using metal powders)will be adjusted to accommodate the requirements of the material.

The materials in the abrasive section of the diamond abrasive grindingwheel of the present invention will include diamond abrasive particles,a thermo-setting bonding resin and the composite powder lubricatingmaterial defined by a graphite particle core disposed within a metalenvelope. It should be observed that supplementary abrasive particlesalso may be used such as, for example, an aluminum oxide. The use of thesupplementary abrasive particles is a matter of choice for themanufacturer and forms no part of the present invention.

The diamond abrasive particles may be natural diamonds or synthesizeddiamonds having a grit size of 80 mesh to 20 micron. One resin that maybe used as the matrix material is a thermosetting plastic materialcommercially available under the trade names Monsanto No. 755 andMonsanto No. 795 both of said resins identified by the trade name hereinbeing generically known as phenol formaldehyde. In one embodiment of theinvention a combination of the above resins was used in a mixturecomprising 15 parts of the No. 755 resin to 10 parts of the No. 795resin. The composite lubricating particles used in one form of theinvention were defined by a graphite core material comprisingapproximately 25% by weight of the composite particle and 75% by weightnickel in the envelope surrounding the graphite lubricating particle. Aparticle of this composition is approximately 43% nickel and 57%graphite core material, by volume. The average particle size of thelubricating medium is about 280 mesh. It should be observed thatgrinding wheels have been made using lubricating particles of difiieringcompositions. For example, in another mode of the invention metal coatedgraphite particles were employed comprising approximately 85% nickel andgraphite by weight.

One method of making the abrasive wheel of the present invention will bedescribed in connection with the use of the apparatus shown in FIGURES 1and 2 of the drawings. It should be observed, however, that other meansmay be used to prepare the abrasive wheel which are different from thedevice schematically represented in FIGURES 1 and 2.

A generally circular mold 10 is provided which forms part of the meansfor forming the abrasive wheel disclosed herein. A generally circularopening 12 is defined in the mold 10. A wheel base member 14 is receivedwithin the opening 12 of said mold. The wheel base 14 defines a recess16 and a core section 18.

The diamond abrasive particles, thermosetting bonding resin matrix andmetal coated graphite lubricating particles are premixed in the desiredratio and a predetermined amount thereof then is placed in the annularopening 20 defined by the walls of the recess 16 of the wheel base 14and the inner periphery of the opening 12 of mold 10. A sufficientamount of the mixture of materials is inserted in the annular opening 20so that the upper surface is approximately flush with the upper surfaceof the core 18.

It should be observed that a metal powder may be used as the matrixmaterial in which case the diamond abrasive particles and the coatedgraphite particles will be mixed with the metal powder. The mixture willbe processed in much the same manner as that set forth herein for theresin matrix except that the metal powder must be sintered to bond it tothe particles of the mixture and to the wheel base. This sinteringtemperature may vary depending upon the powder used as a matrixmaterial. However, the temperatures in sintering or in use should notexceed about 2000 F. to avoid break-down of the coated graphite partices which serve to lubricate the wheel-work interface.

A ram member then is brought down upon the upper surface of the mixtureM to compress the materials within the opening defined by the recess 16and the inner surface 12. A compressive force of approximately 3000 lbs.per. sq. inch is exerted upon the ram 22 and thereby upon the mixture Mwithin the recess 16. The temperature of the assembly then is raised toapproximately 215 degrees Fahrenheit while maintaining the pressure ofabout 3000 lb. per sq. inch upon the mixture M. When the temperature ofabout 215 degrees Fahrenheit has been reached for the assembly heatingof the assembly is terminated and the pressure maintained while theassembly temperature drops to ambient temperature levels. The wheel baseand mixture M (which is now bonded to the base) is removed from the mold10 and is heated for approximately 20 hours at about 300 degreesFahrenheit. This will cure the resin matrix and permanently secure themixture M to the wheel base 14. After curing the wheel base is machinedto remove the core and central portion as schematically illustrated at25 in FIGURE 4. In this manner means will be provided for securing thefinished abrasive wheel to a mandrel or other power source.

As shown in FIGURE 5 of the drawings, the metal coated graphitelubricating particles 32. are generally dispersed in the intersticesbetween the diamond abrasive particles 30 in the mixture M. It should beobserved, of course, that the particles 30 and 32 are bonded to andsecured with the resin matrix.

The form of the metal coated graphite lubricant particles 32 isschematically represented in FIGURE 6 shown in section. As seen inFIGURE 6 the graphite particle is disposed within the metal envelope 38.The composite powder used in the abrasive wheel of the present inventiongenerally consists of a core material (in this specific intance,graphite) coated with a metallic substance which may be nickel or cobaltmetal. In general, the coating process for the composite powdersinvolves hydrogen reduction of a metal from a metal bearing solutiononto a suspended core material, as disclosed in U.S. Patents 2,853,398and 3,062,680. It should be observed that many different combinations ofcomposite powders may be prepared. Core materials ranging in particlesize from .5 micron to Az-inch in diameter may be coated and the coatingthickness is readily variable. It has been suggested that minimumcoating thicknesses of one to two microns is necessary to providesatisfactory coverage of the core material.

Many different mixture compositions may be used in the preparation ofabrasive wheels in accord with the present invention. Some of thecompositions are presented below as follows where all percentages are byvolume unless otherwise stated.

EXAMPLE I An abrasive wheel may be prepared by bonding a mixture M to analuminum wheel base, said mixture having the following composition:

Percent by volume Diamond abrasive (180/220 grit) 25 Resin #755,10%#795) 25 Aluminum oxide abrasive (180/220 grit) Composite lubricantparticle (43% Ni, 57% graphite) 30 EXAMPLE II In another form of theinvention as abrasive wheel may be prepared by bonding a mixture M to analuminum wheel base, said mixture having the following composition:

Percent by volume Diamond abrasive (180/220 grit) Resin (15% #755, 15%#795) Composite lubricant particle (43% Ni, 57% graphite) 45 EXAMPLE IIIAn abrasive Wheel also may be prepared by bonding the mixture M to analuminum wheel base, said mixture having the following composition:

Percent by volume Diamond abrasive (180/220 grit) 25 Resin (15%, #755,10% #795) 25 Composite lubricant particle (43% Ni, 57% graphite) 50EXAMPLE IV An abrasive wheel may be prepared by bonding a mixture M toan aluminum wheel base, said mixture having the following composition:

Percent by volume Diamond abrasive (180/220 grit) 12.5

Resin (15% #755, 10% #795) 25 Composite lubricant particle (43% Ni, 57%graphite) 60 EXAMPLE V While a specific embodiment of the presentinvention is shown and described it will, of course, be understood thatother modifications and alternative constructions may be used withoutdeparting from the true spirit and scope of the invention. It isintended by the appended claims to cover all such modifications andalternative constructions as fall within their true spirit and scope.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An improved abrasive wheel of the type having diamond abrasiveparticles comprising: a phenol formaldehyde thermosetting matrixmaterial; diamond abrasive particles dispersed throughout the matrix inrandom manner and secured in the wheel form by said matrix; and acomplete matrix entrapped solid lubricant material for said wheeldefined by graphite particles having a metallic coating thereabout, saidmetallic coating defining means for bonding the graphite lubricantparticles within the matrix and being dispersable in use to permit flowof the graphite particles over the surface of the diamond abrasiveparticles said metallic coating selected from the group consisting ofnickel or cobalt.

2. The wheel of claim 1 wherein the percentages by volume of thematerials in the wheel may be about:

Percent Diamond abrasive particles 12.5 to 25 Matrix 15 to 30 Metalcoated graphite lubricant 30 to 62.5

3. The wheel of claim 1 wherein the diamond abrasive particles are ofapproximately /220 grit size.

4. The wheel of claim 1 wherein the graphite lubricant material includesa metallic coating approximately several microns in thickness.

5. The wheel of claim 1 wherein the metallic coating of the graphitelubricant material is nickel.

6. The wheel of claim 5 wherein the composite lubricant material isabout 43% by volume nickel as the metallic coating and about 57% byvolume graphite.

7. A method for preparing an improved abrasive wheel of the type havingdiamond abrasive particles secured in a phenol formaldehydethermosetting resin matrix and having a nickel or cobalt coated graphitelubricant material dispersed in said matrix, said method including thesteps of:

mixing together in the resin matrix the diamond abrasive particles andthe metal coated lubricant particles;

placing the mixed materials onto a wheel base of the desired supportcharacteristics and physical dimens1ons; compressing the mixture ofmaterials onto the wheel base with approximately 3,000 p.s.i.g.pressure;

heating the mixture of materials and at least the adjacent wheel basearea to about 215 F.; and

heating the wheel base and mixture of materials thereon to a giventemperature for a time sutficient to cure the thermosetting resin matrixand secure the diamond abrasive particles and metal coated lubricantparticles therein.

8. The method of claim 7 wherein the materials are permitted to coolafter heating to about 215 F. while maintaining compression of thematerial.

9. The method of claim 7 wherein the wheel base and mixture of materialsis maintained at about 300 F. for approximately 20 hours to cure theresin.

10. The method of claim 7 wherein the mixed materials are placed into arecess in the wheel base prior to bonding thereto.

References Cited UNITED STATES PATENTS 2,367,995 1/ 1945 Buckey 512953,062,633 11/1962 Coes 51295 3,168,387 2/1965 Adams 51295 3,316,0734/1967 Kelso 51295 3,317,295 5/ 1967 K'uzrnick 51308 3,321,287 5/ 1967Hunsberger et a1 51308 DONALD J. ARNOLD, Primary Examiner.

